This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In order to meet consumer and industrial demand for natural resources, companies often invest significant amounts of time and money in searching for and extracting oil, natural gas, and other subterranean resources from the earth. Particularly, once a desired subterranean resource is discovered, drilling and production systems are often employed to access and extract the resource. These systems may be located onshore or offshore depending on the location of a desired resource.
Further, such systems generally include a wellhead assembly through which the resource is extracted. These wellhead assemblies may include a wide variety of components that control drilling and/or extraction operations. Such components may include one or more production trees (often referred to as “Christmas trees”), control modules, a blowout preventer system, and various casings, valves, fluid conduits, and the like, that generally facilitate the extraction of resources from a well for transport to the surface. As can be appreciated, production trees often include certain elements for flow monitoring and control, such as choke valves (often referred to as a “choke”) and flow meters, as well as chemical injection metering valves, various sensors, and so forth.
During the resource extraction process, the flow rate of resources extracted from the well may be regulated using flow control devices, such as a valve. Generally, valves for regulating flow rate are controlled using an actuator. For instance, a choke may include a stem that is designed to be stroked along a linear path between an open position and a closed position using a linear actuator designed to apply a force to drive a load (e.g., the choke stem) in a linear direction. For example, the actuator may control the position of the stem to the open position, the closed position, or to an intermediate position between the open and closed position depending on a desired flow rate. Typically, a maximum flow rate is achieved through the choke when the stem is controlled to the open position, and a minimum flow rate is achieved through the choke when the stem is controlled to the closed position. Additionally, intermediate flow rates may be achieved by controlling the stem to an intermediate position (e.g., one that is between the open and closed positions).
Actuators employed in resource extraction applications typically include an input driving mechanism, such as a hydraulic or electric motor. For example, the motor may provide a rotational force that is used to drive one or more gear sets of the actuator. A linear actuation device may then convert rotary motion generated by the gear set(s) into linear motion for driving a load, such as the stem of a valve, to control flow rate. As can be appreciated, such actuators are typically designed with certain parameters suitable for extreme conditions that are often associated with onshore or offshore resource extraction applications. For instance, in an offshore subsea application, it may be desirable to provide an actuator capable of operating under high pressure conditions, such as several thousand pounds per square inch (PSI) of pressure, and of holding high dynamic thrust loads and static loads (e.g., 20,000 pounds or greater) while also being able to fully stroke a load, such as the stem of a choke valve, from an open position to a closed position within a relatively short amount of time (e.g., 5 to 10 minutes).
Some existing actuators may be capable of meeting such operating conditions, but typically require an amount of power that exceeds that which is available from most conventional subsea electronic control systems. A separate higher power system for providing dedicated power to drive such an actuator may be required, which adds to both the complexity and costs associated with subsea resource extraction. Additionally, some existing actuators may be susceptible to back-driving under certain conditions. For instance, when fluid pressure acting on a stem of a choke is great enough, the stem may be forced from a closed or intermediate position towards the open position. As a result, the gear set(s) and motor of the actuator may experience back-driving, which is generally undesirable.